Wet capacitors are used in the design of circuits due to their volumetric efficiency, stable electrical parameters, high reliability and long service life. Such capacitors typically have a larger capacitance per unit volume than certain other types of capacitors, making them valuable in high-current, high-power, and low-frequency electrical circuits. One type of wet capacitor is a wet electrolytic capacitor. A wet electrolytic capacitor includes two conducting surfaces (an anode and a cathode) whose function is to conduct electricity, and a fluid electrolyte. An insulating material or dielectric separates the two conducting surfaces. Wet electrolytic capacitors tend to offer a good combination of high capacitance and low leakage current.
Wet electrolytic capacitors are basic to various types of electrical equipment from satellites, aerospace, airborne, military group support, oil exploration, power supplies, and the like. In any of these example applications, the capacitor may be exposed to harsh environmental conditions, including extreme temperatures, pressure, moisture, shock, vibration, and the like. The capacitor must be able to withstand these harsh environmental conditions while maintaining its accuracy, service life, and ability to be powered at very high temperatures with no maintenance. Failure of a capacitor due to harsh environmental conditions would necessitate its removal for repairs, which would result in delays and other associated expenses. Additionally, many of these example applications include significant dimensional or layout constraints, as the field of electronics is consistently demanding smaller parts and devices. For example, reductions in both mounting area and component profile (i.e., height) are highly demanded in most current applications.
Known wet electrolytic capacitors, such as Tantalum (Ta) electrolytic capacitors, are generally characterized as having a cylindrical shape and axial leaded terminations. Tantalum electrolytic capacitors known in the art may use tantalum for the anode material. The tantalum anode body (also commonly referred to as a “slug” or “pellet”) is usually sintered. A wire (which may also be formed of tantalum) is commonly formed in the anode body in one of two ways: (1) “embedded,” meaning the wire is covered with tantalum powder during a pressing process; or (2) “welded,” meaning after the pellet is pressed and sintered, the wire is welded to the tantalum anode body. The other end of the wire extends outside of the tantalum anode body. The capacitor dielectric material may be made by anodic oxidation of the anode material to form an oxide layer over the surface of the anode body (e.g., Ta to Ta2O5). A capacitor cathode may be formed by coating an inner surface of the body or case of the capacitor that encloses the tantalum anode body. The cathode may be formed of sinter tantalum or electrophoretically deposited tantalum, and may be attached to a cathode wire. A fluid electrolyte separates the cathode and the anode body and provides for electrical communication between the cathode and anode body. Although cylindrical shaped capacitors with axial leaded terminations generally perform reliably in harsh environmental conditions, their provided energy density is limited by their cylindrical shape and limited surface area of their conducting surfaces (anode and cathode), as the surface area of the two conducting surfaces determines the capacitance of the capacitor. Additionally, dimensional constraints often make their application difficult.
Other types of known wet electrolytic capacitors are characterized as having a circular or square shaped capacitor body or “can” with radial leaded terminations. While circular or square shaped capacitors with radial leaded terminations may provide higher energy density when compared to cylindrical shaped capacitors with axial leaded terminations, their ability to operate in harsh environmental conditions is limited. For example, circular or square shaped capacitors with radial leaded terminations generally are more susceptible to elevated temperatures that cause capacitor swelling. Additionally, circular or square shaped capacitors with radial leaded terminations generally have limited ability to survive in high shock or vibration environments.
Thus, there remains a need for an improved wet electrolytic capacitor capable of operating in harsh environmental conditions characterized by high energy density and a low profile to comply with common dimensional constraints.